TechnicalNote Geophysics for On-Shore Wind Energy Developments
A combination of magnetic, ground conductivity and microgravity surveys are used to map archaeological features as well as other geo-hazards such as buried structures, mine workings, solution features, voids and fracture zones. Resistivity tomography surveys are used to provide information on the shallow geology and soil electrical properties for earthing design. This approach is more accurate than the traditional 4-pin method since it is possible to derive more reliable resistivity values. Thermal properties of the soil can be analysed by using a thermal resistivity meter to acquire data either at surface, or within trial pits.
Seismic refraction survey Conductive till 0
20
Resistivity (Ohm.m) 100 200
25
,
Archaeological Surveys
,
Rock Head and Ground strength Surveys
,
Geotechnical information
,
Earthing Measurements
Chainage (m) 30
35
40
Resistive bedrock
45
50
55
60
300
Increasing resistivity
0
Surface gravels
Elevation
“a” Spacing
20
40
60 Test 1 Test 2 80
*Cost Effective *Non-invasive *Rapid Ground Coverage *Environmentally Friendly *Swift Mobilisation/Global Coverage
Seismic surveys provide information on the depth and strength (rippability) of underlying ground materials. Seismic data is acquired using surface-based P and S-wave refraction and /or MASW techniques. On sites with limited survey area or variable geology, seismic data can be obtained from boreholes. By combining the derived seismic P and S-wave velocities with density information, it is possible to calculate Poisson’s Ratio and a range of elastic moduli, i.e. Shear, Young’s and Bulk.
Wind Energy
Over recent years TerraDat has gained a wealth of experience providing geophysical services to the Wind Energy industry. By working alongside many major wind farm developers, TerraDat has developed a suite of geophysical techniques ideally suited to the needs of most onshore wind farm developments. Through maximal understanding of the subsurface, these techniques allow optimisation of turbine location and foundation design.
Resistivity vertical electrical sounding (left) and tomographic section (right) 0m
10m
20m
30m
40m
105 410m/s
810
100
810m/s
810m/s
95
580 550 520 490 460 430 400 370 340 310 280 250 220 190
Increasing ground stiffness
Elevation (m)
P-wave velocity Model
Shear Wave Velocity (m/s)
110
160
2340m/s
MASW S-Wave Model
130 100
P-wave refraction (Layered velocity model) and MASW (S-Wave) Contact Simon Hughes for more info; simon@terradat.co.uk simon@terradat.co.uk
TerraDat (UK) Ltd - Tel (08707 303050) www.terradat.co.uk